The present invention relates to distance measuring equipment and more particularly to a multichannel distance measuring ranging circuit which allows monitoring of multiple DME ground stations.
Distance measuring equipment (DME) is well known in the art, and has been used extensively in commercial aircraft to provide range and velocity information to aircraft interrogating a ground station. Distance measuring equipment has been used in conjunction with VOR equipment to fix the position of an aircraft with respect to a known ground station in accordance with well-known principles. More particularly, the VOR equipment is used to determine the bearing of an aircraft with respect to a given ground station and the DME is used to fix the range of the aircraft from that same ground station. With the bearing and range of the station identified, the location of the aircraft with respect to the ground station can be determined.
While VOR and DME equipment has been used successfully to determine aircraft position, there are inherent inaccuracies produced by VOR equipment which reduces the accuracy of that determination. Modern digital techniques have been implemented in the DME devices, however, which have vastly improved the accuracy of that equipment. Accordingly, since it is known that the same position determination can be made with at least three DME's, it has been suggested that such DME's be used to provide aircraft position determinations rather than one DME and one VOR. It will be appreciated, however, that multiple DME's are expensive and take up aircraft space which might otherwise be used for other instrumentation. Accordingly, the use of a single DME to fix aircraft position is highly desirable in current commercial and private aircraft.
In the prior art, there have been attempts to obviate the need for multiple DME's by multiplexing a single DME to obtain multichannel operation. In particular, U.S. Pat. No. Re. 30,069 issued to Wayne Miller on Aug. 7, 1979, discloses a multiranging DME system which time multiplexes a DME between two channels which allows reception of multiple frequency inputs from two separate ground stations. While this technique expands the application of the DME to more than one ground station, the known technique primarily uses one channel to obtain distance and velocity information and the other channel to obtain distance information. As a result, aircraft position may still be ambiguous and another DME would be required to electronically resolve the ambiguity in aircraft position. In addition, the operation of the channels is not independent and is incapable of providing velocity and identity information for each of the selected ground stations.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known techniques and to provide an improved DME ranging system capable of providing multichannel operation to provide accurate aircraft position and velocity determinations.